Raw steel and tin-plated panels must be coated with paint or polyurethane soon after they're installed, to prevent rust. First, clean the surface with denatured alcohol. Then, if painting, brush, roll, or spray on an oil-based, rust-inhibiting primer followed by at least one coat of oil or latex paint. If you want to play up the metal's silvery appearance, apply two coats of an oil-based poly instead. For humid bathrooms, make sure to coat the back of the panels before installing them.